1. Field of the Invention
The present invention generally relates to a vertical-type metal insulator semiconductor field effect transistor (MISFET) device, and a production method for manufacturing such a vertical-type MISFET device.
2. Description of the Related Art
As well known, a metal insulator field effect transistor (MISFET) device is represented by a metal oxide semiconductor field effect transistor (MOSFET) device, and there are two types of MOSFET devices. One type of the MOSFET device is disclosed in, for example, JP-A-H10-270693, and is frequently called a horizontal-type MOSFET device in which a drain current flows horizontally in parallel with the plane of a semiconductor substrate. The other type of the MOSFET device is disclosed in, for example, in JP-A-H10-173178, and is frequently called a vertical-type MOSFET device in which a drain current flows vertically, perpendicularly to the plane of a semiconductor device.
The vertical-type MOSFET device is frequently used as a power MOSFET device, because a large amount of drain current can be obtained. In particular, the vertical-type MOSFET device includes a plurality of unit transistor cells (MOSFET) produced and arranged in the semiconductor substrate, and the plurality of unit transistor cells function as a MOSFET. Thus, in the vertical-type MOSFET device, it is possible to obtain a large total amount of drain current.
One of the significant factors for evaluating the vertical-type power MOSFET device is responsivity to application of voltage to a gate electrode in the vertical-type power MOSFET device. In general, the smaller a gate-drain capacitance in the vertical-type power MOSFET device, the higher the responsivity for driving the vertical-type power MOSFET device at a higher speed.
Also, as well known, an ON-resistance and a breakdown voltage in the vertical-type power MOSFET device form significant factors for evaluating the vertical-type power MOSFET device. The smaller the ON-resistance, the higher the evaluation of the vertical-type power MOSFET device. Nevertheless, in general, as the ON-resistance becomes smaller, the breakdown voltage is lowered. Namely, the decrease of the ON-resistance is incompatible with the increase of the breakdown voltage.
In the vertical-type power MOSFET device disclosed in JP-A-H10-173178, a gate-drain capacitance is relatively small, and thus it features an inferior responsivity to application of voltage to a gate electrode, as stated in detail hereinafter. Namely, the vertical-type power MOSFET device concerned cannot be driven at a higher speed. Also, the vertical-type power MOSFET disclosed in JP-A-H10-173178 fails to feature a high breakdown voltage, as stated in detail hereinafter.